Both the Otto and Diesel cycle engines accomplish their purposes via parameters or strokes, which follow one another in a defined order: (1) intake stroke, (2) compression stroke, (3) power or firing stroke, and (4) exhaust stroke. Each of these four parameters are performed in each power cylinder of a multi cylinder Otto or Diesel cycle engine. Each of these cycles can be further classified as a "two-stroke cycle" which achieves all of these parameters or "strokes" in one revolution of the crank shaft, or "four stroke cycle" which achieves all of these parameters or "strokes" in two revolutions of the crank shaft.
In a four stroke internal combustion engine operating on the Otto cycle, a mixture of air and vaporized fuel is inducted or forced into a combustion cylinder or cylinders when the piston is traveling downward on the intake stroke. The mixture is compressed as the piston comes up on the compression stroke. The mixture is then ignited by a spark plug at or near top dead center of the piston. Combustion takes place at a constant volume creating a high pressure and temperature in the cylinder thereby forcing the piston down and producing work. According to Benson, Rowland and Whitehouse, N.D., "Internal Combustion Engines," New York: Pergamon Press, 1979, p 17, the normal total duration of combustion is usually about 30.degree.-40.degree. crank angle. It can be seen in FIG. 9, however, that the combustion pressure remains substantially constant for only a very short crank angle duration. After the piston reaches the bottom of the cylinder, the burned gases are exhausted from the cylinder through an open valve by the piston on its last stroke up in the cylinder. After the exhaust stroke, the entire procedure repeats itself continuously until the process is interrupted usually by opening the electrical circuit of the spark plug.
In a four stroke internal combustion engine operating on the Diesel cycle, air is inducted or forced into a combustion cylinder or cylinders when the piston is traveling downward on the intake stroke. The air is compressed as the piston comes up on the compression stroke. Fuel is injected at or near top dead center of the piston and continues to a predesignated stopping point usually around 15.degree.-20.degree. after top dead center. Combustion takes place at a constant pressure creating a high pressure and temperature in the cylinder thereby forcing the piston down and producing work. According to Heywood, John B., "Combustion Engine Fundamentals," New York: McGraw-Hill Book Company, 1988, p. 493, the normal total duration of combustion is usually about 40.degree.-50.degree. crank angle. It can be seen in FIG. 10, however, that the combustion pressure remains substantially constant for only a very short crank angle duration. After the piston reaches the bottom of the cylinder, the burned gases are exhausted from the cylinder through an open valve by the piston on its last stroke up in the cylinder. After the exhaust stroke, the entire procedure repeats itself continuously until the process is interrupted usually by stopping the flow of the fuel.
Each of the above type of engine can be provided as naturally aspirated, supercharged or turbocharged, intercooled and/or after cooled. Superchargers and turbochargers both allow more mass of air to be trapped within a given engine size, bore, stroke, and rpm. Intercoolers and aftercoolers also allow more air to be trapped in a given engine size, bore and rpm.
In general, more air mixed with more fuel at a combustible air fuel ratio allows an engine to produce more brake horsepower (Bhp) output. Other than exceeding mechanical design limitations, the only end point to producing more and more Bhp from an Otto or Diesel cycle engine by introducing more air and more fuel to any given engine is detonation.
Detonation occurs when the unburned air/fuel mixture ahead of the flame front is heated to its autoignition temperature. Then, all of the unburned mixture can burn up in less than a thousandth of a second. This is comparable to an explosion, and peak firing pressures of several hundred psi can become several thousand psi, damaging or destroying the engine. Therefore, for any Otto cycle as well as any Diesel cycle engine, the limit of increasing horsepower via adding more and more air fuel mixture to any such engine is detonation. The autoignition temperature for various fuels is readily available and shown in the following table from J. H. Perrys ChE Handbook, pp. 9-31 through 9-33.
TABLE 1 ______________________________________ Tabulation of Autoignition Temperatures -- Various Hydrocarbons at Atmospheric Pressure Fuel Formula A.I.T., .degree.F. ______________________________________ Methane CH.sub.4 1170 Ethane C.sub.2 H.sub.6 882 Propane C.sub.3 H.sub.8 940 N-Butane C.sub.4 H.sub.10 807 N-Pentane C.sub.5 H.sub.12 544 N-Hexane C.sub.6 H.sub.14 501 N-Heptane C.sub.7 H.sub.16 477 N-Octane C.sub.8 H.sub.18 464 Gasoline 73 Octane 570 Gasoline 100 Octane 800-950 ______________________________________